I use colors a lot to help organize my calculations and this feature would help a lot as I don't always think of the clearest color scheme at my first attempt.
Perhaps it could be implemented in your code by tagging and linking to colors, which could then be changed, just on a single page, rather than labelling with the color directly, if that's how you currently do it. Presumably you would have to limit it in some way, perhaps with an on/off switch or confining it to a customizable color palette, as I guess it might otherwise cause efficiency problems for users who use random or a very large number of colors.
Thanks for an (almost!) perfect app.